The present invention relates generally to a compressor blade clearance measurement system, and more particularly to a system for use in jet engine test facilities for clearance measurement between rotating blades and case.
Measurement of blade-case clearance on an operating jet engine has always been a difficult task to accomplish accurately. Accuracy, stability and reliability under the harsh conditions imposed by an operating engine have been less than desirable on past systems. The need for this data becomes more important as the requirement for higher efficiency and performance are sought.
U.S. Pat. No. 3,504,279 discloses a system for the noncontact inspection of a rotating interrupted surface which includes pickup sensitive to distince dependent energy variation signal processing circuitry and display means to provide a visual analog of the profile of the surface under inspection. U.S. Pat. No. 4,086,528 discloses a measuring apparatus for determining a linear quantity which includes a capacitance transducer. Soviet Union Pat. No. 667,800 discloses an apparatus for measuring the dynamic radial gap in rotating electrical machines and turbines using a capacitive transducer. West German Pat. No. 1,249,290 discloses a test rig for turbine blades to check that none is missing, which includes an electrode in the turbine housing close to the rotating blade wheel rim to produce a modulated signal as each blade passes.